Local fix

Problem summary

System configured with ethernet, SANCOM and DPCOM may Panic
with "Deadman timer triggered." panic string when ethernet
is disabled and SANCOM is experiencing outgoing EOVERFLOW
transmission errors.

Problem conclusion

Normally it is expected the cluster would fall back to
DPCOM in such cases, but that was not happening because
the SANCOM interface was not being marked DOWN even though
it was experiencing transmission issues.
Fixed monitoring of SANComm traffic such that if there is
none, it is marked DOWN, leading to enablement of DPCOM.